Neutral pion photoproduction on the nucleon in a chiral quark model

作者：Xiao, Li-Ye; Cao, Xu; Zhong, Xian-Hui^*

来源：Physical Review C, 2015, 92(3): 035202.

DOI：10.1103/PhysRevC.92.035202

• POLARIZED TARGET ASYMMETRY
• RECOIL-PROTON POLARIZATION
• BARYON RESONANCES
• PI(0) PHOTOPRODUCTION
• ETA-PHOTOPRODUCTION
• ANGULAR-DEPENDENCE
• PHOTON ENERGIES
• REGION
• HYDROGEN
• GAMMA

Achiral quark-model approach is adopted to study the gamma p -> pi(0) p and gamma n -> pi(0) n reactions. Good descriptions of the total and differential cross sections and single-polarization observables are obtained from the pion production threshold up to the second resonance region. It is found that (i) the n = 0 shell resonance Delta(1232)P-33, the n = 1 shell resonances N(1535)S-11 and N(1520)D-13, and the n = 2 shell resonance N(1720)P-13 play crucial roles in these two processes. They are responsible for the first, second, and third bump structures in the cross sections, respectively. (ii) Furthermore, obvious evidence of N(1650)S-11 and Delta(1620)S-31 is also found in the reactions. They notably affect the cross sections and the polarization observables from the second resonance region to the third resonance region. (iii) The u-channel background plays a crucial role in the reactions. It has strong interferences with the s-channel resonances. (iv) The t-channel background seems to be needed in the reactions. Including the t-channel vector-meson exchange contribution, the descriptions in the energy region E-gamma = 600-900 MeV are improved significantly. The helicity amplitudes of the main resonances, Delta(1232)P-33, N(1535)S-11, N(1520)D-13, N(1720)P-13, N(1650)S-11, and Delta(1620)S-31, are extracted and compared with the results from other groups.

• 出版日期2015-9-8
• 单位湖南师范大学; 中国科学院近代物理研究所